Process for producing polyarylene sulfide

ABSTRACT

In the dehydration step, a mixture comprising an organic amide solvent and a sulfur source is heated, vapor volatilized is guided to a distillation column, a fraction comprising the organic amide solvent as a principal component is refluxed into a reaction vessel, a fraction comprising water and hydrogen sulfide is cooled to discharge hydrogen sulfide that is not condensed by the cooling and reflux a part of water condensed into the distillation column, the remaining water is discharged, a relational expression between the total amount of water of an amount of water refluxed and an amount of water discharged without being refluxed, and an amount of hydrogen sulfide discharged from the reaction vessel is determined in advance, and an amount of hydrogen sulfide discharged from the reaction vessel is calculated out from a measured value of the total amount of water on the basis of the relational expression to control a charged molar ratio of the sulfur source to a dihalo-aromatic compound.

TECHNICAL FIELD

The present invention relates to a production process of a poly(arylenesulfide), and particularly to a production process of a poly(arylenesulfide), by which a poly(arylene sulfide) having a desired meltviscosity can be stably produced.

BACKGROUND ART

Poly(arylene sulfides) (hereinafter abbreviated as “PASs”) representedby poly(phenylene sulfide) (hereinafter abbreviated as “PPS”) areengineering plastics excellent in heat resistance, chemical resistance,flame retardancy, mechanical properties, electrical properties,dimensional stability and the like. The PASs are commonly used in a widevariety of fields such as electrical and electronic equipments andautomotive equipments because they can be formed or molded into variouskinds of molded or formed products, films, sheet, fibers, etc. bygeneral melt processing techniques such as extrusion molding, injectionmolding and compression molding.

As a typical production process of a PAS, is known a process, in whichan alkali metal sulfide that is a sulfur source is reacted with adihalo-aromatic compound in an organic amide solvent such asN-methyl-2-pyrrolidone. As the sulfur source, a combination of an alkalimetal hydrosulfide and an alkali metal hydroxide is also used.

In order to stably provide a good-quality PAS, it is necessary tostrictly control polymerization conditions such as a molar ratio of analkali metal sulfide to a dihalo-aromatic compound, a water content, apolymerization temperature and polymerization time on the premise thatthe purities of raw materials, secondary raw materials and the like arehigh and constant. For example, if a water content in the polymerizationreaction system is too low, unpreferable reactions such as decompositionof a PAS formed tend to occur. If the water content is too high to thecontrary, a polymerization rate is markedly slowed, or unpreferable sidereactions are caused.

As the alkali metal sulfide of a raw material, is generally used itshydrate containing a great amount of water of crystallization. Further,these raw materials may be added to the reaction system as aqueoussolutions in some cases. Accordingly, a great amount of water exists inthe system at the point of time these raw materials have been chargedinto a reaction vessel. Upon the production of a PAS, thus, adehydration step of heating and dehydrating a mixture containing anorganic amide solvent and a sulfur source to control a water content inthe polymerization reaction system is generally arranged as a step priorto a polymerization step.

The dehydration step is generally operated in the presence of an organicamide solvent that is a solvent for polymerization reaction andconducted until water is discharged out of the system by distillation,and the water content is lowered to generally 0.3 to 5 mol, preferably0.5 to 2.0 mol per mol of the alkali metal sulfide. When the watercontent has become too low in the dehydration step, water is added priorto the polymerization reaction to regulate the water content within adesired range. After the water content is regulated, a dihalo-aromaticcompound is charged into the reaction system, and the reaction system isheated, thereby conducting a polycondensation reaction.

In the dehydration step, the alkali metal sulfide reacts with water inthe organic amide solvent, and hydrogen sulfide (H₂S) is equilibriouslydissociated and volatilized out. When water is distilled off by heatingin the dehydration step, the water is discharged together with theorganic amide solvent outside the system, or the organic amide solventand water are separated from each other by distillation, and only wateris discharged. At the same time, hydrogen sulfide formed is alsovolatilized out and discharged outside the system. The volatilization ofhydrogen sulfide in the dehydration step causes the following problemsin an industrial production process of a PAS.

First, since the amount of a sulfur source such as an alkali metalsulfide is varied by the volatilization of hydrogen sulfide, meltviscosities of product polymers vary every lot. In general, the qualityof polymers formed of every lot varies according to, for example, achange of raw materials (particularly, an alkali metal sulfide and/or analkali metal hydrosulfide), variations in the composition of rawmaterials attending on changes in the grade of PAS, or variations in theamount of hydrogen sulfide volatilized out attending on changes in therate of dehydration under heat or changes of reflux ratio in adistillation column. In addition, even when the same raw materials areused, and production is performed under substantially the sameconditions, melt viscosities of polymers formed vary between lotsbecause the amount of hydrogen sulfide volatilized out in thedehydration step varies.

Second, it is difficult to stably produce a PAS having a highpolymerization degree due to volatilization of hydrogen sulfide. Forexample, since a way of polymerization reaction between an alkali metalsulfide and a dihalo-aromatic compound is a polycondensation reactionbetween 2 components, it is generally desirable to regulate a molarratio between both components to about 1:1 with high accuracy in orderto provide a PAS having a high polymerization degree. Thus, the amountof hydrogen sulfide volatilized out in the dehydration step is predictedto control the amount of a sulfur source (alkali metal sulfide and/oralkali metal hydrosulfide) charged. However, it is difficult to controlan accurate molar ratio between both components upon the reactionbecause the range of variations in the amount of hydrogen sulfidevolatilized out is wide.

If the amount of hydrogen sulfide actually volatilized out is less thanthe predicted amount, a molar ratio of the alkali metal sulfide to thedihalo-aromatic compound becomes excessive, and so undesirable sidereactions such as rapid decomposition reaction tend to occur. In orderto stably produce a PAS having a high polymerization degree, thus, it isessential to strictly control and measure the amount of hydrogen sulfidevolatilized out. However, it has been difficult to achieve the intendedmelt viscosity and thin a scatter of melt viscosity because the amountof hydrogen sulfide volatilized out in the dehydration step varies.

Some proposals have heretofore been made for the purpose of solving theproblems attending on the volatilization of hydrogen sulfide in thedehydration step. For example, there has been proposed a processcomprising determining the amount of hydrogen sulfide volatilized out ina dehydration step to find an amount of a sulfur source existing thereaction system with high accuracy (for example Japanese PatentPublication No. 33775/1988). According to this process, a molar ratio ofthe alkali metal sulfide to the dihalo-aromatic compound in thepolymerization step may be fitted with high accuracy. However, it isnecessary to introduce a special dedicated device for the determinationof hydrogen sulfide volatilized out in the dehydration step, and thequantitative analysis brings loss of time.

There has been proposed a process causing hydrogen sulfide volatilizedout in a dehydration step to be absorbed in an aqueous solution of analkali metal hydroxide to recycle and reuse it in a dehydration stepand/or a polymerization step of the next batch (for example, JapanesePatent Application Laid-Open No. 160833/1990). When the aqueous solutionof hydrogen sulfide recovered is recycled through the dehydration stepof the next batch, however, this process brings high energy loss becausethe amount of water to be dehydrated increases. When the aqueoussolution of hydrogen sulfide recovered is recycled through thepolymerization step of the next batch, the process involves the problemsattending on a polymerization reaction in the above-described system thewater content in which is high.

There has been proposed a process comprising causing hydrogen sulfidegenerated in a dehydration step to be absorbed in an aqueous solution ofsodium hydroxide and conducting neutralization titration with 1Nhydrochloric acid to determine the amount of hydrogen sulfidevolatilized out (for example, Japanese Patent Application Laid-Open No.160834/1990). However, the process comprising collecting hydrogensulfide in the aqueous solution of sodium hydroxide to determine itrequires to introduce a dedicated device for the determination, andmoreover an operation for determining is newly developed to reduceproduction efficiency. In addition, when the aqueous solution of sodiumhydroxide containing hydrogen sulfide recovered is recycled through thereaction system, problems attending on increase in sodium hydroxide andwater arise from the viewpoints of polymerization reaction and thequality of a PAS to be formed.

There has been proposed a process comprising recovering hydrogen sulfidevolatilized out during a dehydration step by causing it to be absorbedin an organic amide solvent outside the system, in which the dehydrationstep is being conducted, and reusing the hydrogen sulfide recovered as asulfur source in a polymerization reaction (for example, Japanese PatentApplication Laid-Open No. 286861/1997). According to this process, thehydrogen sulfide volatilized out in the dehydration step can berecovered and reused, thereby solving various problems attending on thevolatilization of hydrogen sulfide and producing a PAS little invariation of melt viscosity and stable in quality. However, even in thisprocess, the amount of the volatilized hydrogen sulfide absorbed in theorganic amide solvent varies, and there is a demand for developing amethod for more accurately grasping the amount of hydrogen sulfide.

Among the qualities of a PAS, a melt viscosity is one of the mostimportant qualities. It is known that a charge ratio (hereinafterabbreviated as “P/S ratio”) of a dihalo-aromatic compound to an alkalimetal sulfide strongly affects the melt viscosity of the PAS. However,in a production process of a PAS, comprising adding an alkali metalhydroxide as needed, and heating and polymerizing a dihalo-aromaticcompound and an alkali metal sulfide and/or an alkali metal hydrosulfidein an organic amide solvent, there has not been yet proposed anindustrially adoptable and excellent method for fixedly controlling theP/S ratio.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a production processof a poly(arylene sulfide), by which a poly(arylene sulfide) having adesired melt viscosity can be stably produced.

In particular, an object of present invention is to provide a process bywhich a dehydration step can be smoothly performed, an amount ofhydrogen sulfide lost by volatilization out of the reaction system, orthe like can be extremely accurately calculated out by a comparativelysimple method, and a molar ratio of a sulfur source charged to adihalo-aromatic compound charged is accurately controlled and set on thebasis of the amount calculated out, thereby stably producing apoly(arylene sulfide) having a desired melt viscosity.

The present inventors have carried out an extensive investigation with aview toward achieving the above objects. As a result, the inventors haveconceived of a method for calculating out an amount of hydrogen sulfidedischarged from a reaction vessel in a production process of a PAScomprising a polymerization step of subjecting a sulfur source and adihalo-aromatic compound to a polymerization reaction in an organicamide solvent, wherein in a dehydration step that is a step prior to thepolymerization step, the dehydration step is performed by a processcomprising heating the mixture in the reaction vessel, to which adistillation column is linked, guiding vapor volatilized to thedistillation column to distill and separate it into respectivecomponents, refluxing a high-boiling fraction taken out of the bottom ofthe distillation column and comprising the organic amide solvent as aprincipal component into the reaction vessel, cooling a low-boilingfraction taken out of the top of the distillation column and comprisingwater and hydrogen sulfide on the other hand to discharge hydrogensulfide that is not condensed by the cooling and reflux a part of watercondensed into the distillation column, and discharging the remainingwater, and a relational expression between the total amount of water ofthe amount of water refluxed into the distillation column and the amountof water discharged without being refluxed, and the amount of hydrogensulfide discharged from the reaction vessel is determined in advance,thereby calculating out the amount of hydrogen sulfide discharged from ameasured value of the total amount of water on the basis of therelational expression.

An amount (amount of the sulfur source charged) of the sulfur sourceremaining in the mixture after the dehydration step can be calculatedout on the basis of the amount (amount of hydrogen sulfide discharged)of hydrogen sulfide calculated out by the above-described method,thereby controlling a charged molar ratio of the sulfur source to thedihalo-aromatic compound on the basis of the amount of the sulfur sourcecalculated out. According to this method, the amount of hydrogen sulfidecan be accurately calculated out without collecting hydrogen sulfidedischarged to conduct quantitative analysis, thereby stably producingPASs extremely little in variation of melt viscosity every lot. Thepresent invention has been led to completion on the basis of thesefindings.

According to the present invention, there is provided a process forproducing a poly(arylene sulfide), comprising, after a dehydration stepof heating and dehydrating a mixture containing an organic amidesolvent, at least one sulfur source (A) selected from the groupconsisting of alkali metal hydrosulfides and alkali metal sulfides andan alkali metal hydroxide added as needed to control the amount of waterin the mixture, a polymerization step of charging a dihalo-aromaticcompound (B) into the system containing the remaining mixture to subjectthe sulfur source (A) and the dihalo-aromatic compound (B) to apolymerization reaction in the organic amide solvent, which comprises:

(1) in the dehydration step, heating the mixture containing the organicamide solvent, at least one sulfur source (A) selected from the groupconsisting of alkali metal hydrosulfides and alkali metal sulfides andthe alkali metal hydroxide added as needed in a reaction vessel, towhich a distillation column is linked, and guiding vapor volatilized tothe distillation column to distill and separate it into respectivecomponents,

refluxing a high-boiling fraction taken out of the bottom of thedistillation column and comprising the organic amide solvent as aprincipal component into the reaction vessel,

cooling a low-boiling fraction taken out of the top of the distillationcolumn and comprising water and hydrogen sulfide to discharge hydrogensulfide that is not condensed by the cooling and reflux a part of watercondensed into the distillation column, discharging the remaining water,

(2) determining a relational expression between the total amount ofwater of an amount of water refluxed into the distillation column and anamount of water discharged without being refluxed, and an amount ofhydrogen sulfide discharged in advance, thereby calculating out theamount of hydrogen sulfide discharged from a measured value of the totalamount of water on the basis of the relational expression,

(3) calculating out an amount (hereinafter referred to as “amount of thesulfur source charged”) of the sulfur source (A) remaining in themixture after the dehydration step on the basis of the amount ofhydrogen sulfide calculated out, thereby controlling a charged molarratio of the sulfur source (A) to the dihalo-aromatic compound (B) onthe basis of the amount of the sulfur source (A) calculated out, andthen

(4) subjecting the sulfur source (A) and the dihalo-aromatic compound(B) to the polymerization reaction in the organic amide solvent in thepolymerization step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary apparatus used in the production processaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

1. Sulfur Source:

In the present invention, at least one sulfur source selected from thegroup consisting of alkali metal hydrosulfides and alkali metal sulfidesis used as a sulfur source. As examples of the alkali metal sulfides,may be mentioned lithium sulfide, sodium sulfide, potassium sulfide,rubidium sulfide, cesium sulfide and mixtures of two or more compoundsthereof. These alkali metal sulfides are generallycommercially-available and used in the form of a hydrate. Examples ofthe hydrate include sodium sulfide nonahydrate (Na₂S.9H₂O) and sodiumsulfide pentahydrate (Na₂S.5H₂O). The alkali metal sulfide may be usedas an aqueous mixture.

As a sulfur source, an alkali metal hydrosulfide may be used incombination with an alkali metal hydroxide. As examples of the alkalimetal hydrosulfide, may be mentioned lithium hydrosulfide, sodiumhydrosulfide, potassium hydrosulfide, rubidium hydrosulfide, cesiumhydrosulfide and mixtures of two or more compounds thereof. The alkalimetal hydrosulfide may be used in any form of an anhydride, a hydrateand an aqueous solution. Among these, sodium hydrosulfide and lithiumhydrosulfide are preferred in that they are industrially available onthe cheap. The alkali metal hydrosulfide is preferably used as anaqueous mixture (i.e., a mixture with water having fluidity) such as anaqueous solution from the viewpoints of treatment operation, metering,etc.

In general, a small amount of an alkali metal sulfide is secondarilyproduced in a production process of the alkali metal hydrosulfide. Asmall amount of the alkali metal sulfide may be contained in the alkalimetal hydrosulfide used in the present invention. In this case, thetotal molar quantity of the alkali metal hydrosulfide and alkali metalsulfide becomes a sulfur source charged after a dehydration step.

Examples of the alkali metal hydroxide include lithium hydroxide, sodiumhydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide andmixtures of two or more compounds thereof. Among these, sodium hydroxideand lithium hydroxide are preferred in that they are industriallyavailable on the cheap. The alkali metal hydroxide is preferably used asan aqueous mixture such as an aqueous solution.

In the production process according to the present invention, examplesof water to be dehydrated in a dehydration step includes water ofhydration, a water medium of an aqueous solution and water secondarilyproduced by a reaction of the alkali metal hydrosulfide with the alkalimetal hydroxide, or the like.

2. Dihalo-Aromatic Compound:

The dihalo-aromatic compound used in the present invention is adihalogenated aromatic compound having 2 halogen atoms directly bondedto the aromatic ring.

Specific examples of the dihalo-aromatic compound includeo-dihalobenzene, m-dihalobenzene, p-dihalobenzene, dihalotoluene,dihalonaphthalene, methoxy-dihalobenzene, dihalobiphenyl, dihalobenzoicacid, dihalodiphenyl ether, dihalodiphenyl sulfone, dihalodiphenylsulfoxide and dihalodiphenyl ketone.

Here, the halogen atom means each atom of fluorine, chlorine, bromineand iodine atoms, and 2 halogen atoms in the dihalo-aromatic compoundmay be the same or different from each other. These dihalo-aromaticcompounds may be used either singly or in any combination thereof.

The amount of the dihalo-aromatic compound charged is generally 0.90 to1.50 mol, preferably 0.95 to 1.20 mol, more preferably 1.00 to 1.09 molper mol of the sulfur source (alkali metal sulfide and/or alkali metalhydrosulfide) remaining in the system after the dehydration step.

3. Molecular Weight Adjuster, Branching or Crosslinking Agent:

In order to, for example, form a terminal of a specific structure in aPAS formed or regulate a polymerization reaction or a molecular weight,a monohalo-compound (may not be always an aromatic compound) may be usedin combination. In order to form a branched or crosslinked polymer, apolyhalo-compound (may not be always an aromatic compound), to which atleast 3 halogen atoms are bonded, an active hydrogen-containinghalogenated aromatic compound, a halogenated aromatic nitro compound orthe like may also be used in combination. As the polyhalo-compound as abranching or crosslinking agent is preferred trihalobenzene.

4. Organic Amide Solvent:

In the present invention, an organic amide solvent that is an aproticpolar organic solvent is used as a solvent for a dehydration reactionand a polymerization reaction. The organic amide solvent is preferablystable to an alkali at a high temperature.

Specific examples of the organic amide solvent include amide compoundssuch as N,N-dimethylformamide and N,N-dimethylacetamide;N-alkylcaprolactam compounds such as N-methyl-ε-caprolactam;N-alkylpyrrolidone compounds or N-cycloalkylpyrrolidone compound such asN-methyl-2-pyrrolidone and N-cyclohexyl-2-pyrrolidone;N,N-dialkyl-imidazolidinone compounds such as1,3-dialkyl-2-imidazolidinones; tetraalkylurea compounds such astetramethylurea; and hexaalkylphosphoric triamide compounds such ashexamethylphosphoric triamide. These organic amide solvents may be usedeither singly or in any combination thereof.

Among these organic amide solvents, N-alkyl-pyrrolidone compounds,N-cycloalkylpyrrolidone compounds, N-alkylcaprolactam compounds andN,N-dialkyl-imidazolidinone compounds are preferred, andN-methyl-2-pyrrolidone, N-methyl-ε-caprolactam and1,3-dialkyl-2-imidazolidinones are particularly preferably used.

The amount of the organic amide solvent used in the polymerizationreaction in the present invention is generally within a range of 0.1 to10 kg per mol of the sulfur source.

5. Polymerization Aid:

In order to promote the polymerization reaction to obtain a PAS having ahigh polymerization degree in a short period of time, various kinds ofpolymerization aids may be used in the present invention as needed.Specific examples of the polymerization aids include metal salts oforganic sulfonic acids, lithium halides, metal salts of organiccarboxylic acids and alkali metal salts of phosphoric acid, which aregenerally publicly known as polymerization aids for PASs. Among these,metal salts of organic carboxylic acids are particularly preferredbecause they are cheap.

The amount of the polymerization aid used varies according to the kindof the compound used. However, it is generally within a range of 0.01 to10 mol per mol of the sulfur source charged.

6. Dehydration Step:

The dehydration step is performed by a process comprising heating analkali metal sulfide and/or an alkali metal hydrosulfide in an organicamide solvent in the presence of an alkali metal hydroxide as needed,desirably, under an inert gas atmosphere and discharging water outsidethe system by distillation. Since the alkali metal sulfide is generallyused as a hydrate or aqueous mixture, it contains more water than thepolymerization reaction needs. When the alkali metal hydrosulfide isused as a sulfur source, an alkali metal hydroxide of the order of anequimolar amount is added to allow the alkali metal hydrosulfide toreact therewith in situ in an organic amide solvent.

In the dehydration step, the dehydration is conducted until the contentof water comprising water of hydration (water of crystallization), awater medium, secondarily produced water, etc. is lowered within a rangeof necessary amounts. In the dehydration step, the dehydration isconducted until the water content in the polymerization reaction systemis reduced to generally about 0.3 to 5 mol, preferably about 0.5 to 2mol per mol of the sulfur source. When the water content has become toolow in the dehydration step, water may be added prior to apolymerization step to regulate the water content to a desired value.

The charging of these raw materials into a reaction vessel is conductedwithin a temperature range of generally from ordinary temperature to300° C., preferably from ordinary temperature to 200° C. The charging ofthe raw materials may not be in order, and the respective raw materialsmay be additionally charged in the course of the dehydration process. Anorganic amide solvent is used as a solvent used in the dehydration step.This solvent is preferably the same as the organic amide solvent used inthe polymerization step, and N-methyl-2-pyrrolidone is particularlypreferred. The amount of the organic amide solvent used is generallyabout 0.1 to 10 kg per mol of the sulfur source charged in the reactionvessel.

The dehydration process is conducted by heating the mixture aftercharging the raw materials into the reaction vessel in a temperaturerange of generally up to 300° C., preferably from 100 to 250° C. forgenerally 15 minutes to 24 hours, preferably 30 minutes to 10 hours.Heating methods include a method of retaining a fixed temperature, amethod of raising the temperature either stepwise or continuously and amethod of combining both methods. The dehydration step is conducted by,for example, a batch system, a continuous system or a combined systemthereof. However, the batch system is preferred for the productionprocess according to the present invention.

A reaction vessel for conducting the dehydration step may be the same asa polymerization vessel (reactor) used in the subsequent polymerizationstep or different from it. A material of the reaction vessel ispreferably a corrosion resistant material, with a titanium materialbeing particularly preferred. In the dehydration step, a part of theorganic amide solvent is generally discharged together with wateroutside the reaction vessel. At that time, hydrogen sulfide isdischarged (volatilized out) as a gas.

In the dehydration step, the mixture containing the organic amidesolvent, at least one sulfur source selected from the group consistingof alkali metal hydrosulfides and alkali metal sulfides and the alkalimetal hydroxide added as needed is heated to dehydrate it. In theproduction process according to the present invention, the dehydrationstep is performed in a reaction vessel, to which a distillation columnis linked: The mixture containing the organic amide solvent, at leastone sulfur source selected from the group consisting of alkali metalhydrosulfides and alkali metal sulfides and the alkali metal hydroxideadded as needed is heated in this reaction vessel, and vapor volatilizedis guided to the distillation column to distill and separate it intorespective components. A high-boiling fraction taken out of the bottomof the distillation column and comprising the organic amide solvent as aprincipal component is refluxed into the reaction vessel.

On the other hand, a low-boiling fraction taken out of the top of thedistillation column and comprising water and hydrogen sulfide is cooledand condensed. Hydrogen sulfide that is not condensed by the cooling isdischarged. (volatilized out) as a gas. A part of water condensed by thecooling is refluxed into the distillation column, and the remainingwater is discharged. The remaining water may be stored in a storagetank. In that case, the water refluxed into the distillation column ispassed through, for example, a flowmeter to measure the cumulativeamount thereof. Although the remaining water that is not refluxed intothe distillation column is discharged, the cumulative amount thereof isalso measured. When the whole amount of the remaining water is stored inthe storage tank, the amount of water stored in the storage tank afterthe dehydration step is measured to regard it as a cumulative amount ofwater.

The method according to the present invention in the dehydration stepwill be described more specifically with reference to FIG. 1. FIG. 1illustrates an exemplary apparatus used in the production processaccording to the present invention. An upper part of a reaction vessel(for example, a polymerization vessel) 1, in which a dehydrationreaction is performed, is connected to a distillation column 3 through aline 2 and successively connected to a condenser 5 and a storage tank 6through a line 4 extending from the top of the distillation column 3. Asthe distillation column 3 is desirably used a high performancedistillation column capable of efficiently separating an organic amidesolvent such as N-methyl-2-pyrrolidone and water from each other.

A fraction comprising the organic amide solvent as a principal componentis taken out of the bottom of the distillation column 3. This fractionis refluxed into the reaction vessel 1 through a line 10. A fractioncontaining water and hydrogen sulfide is taken out of the top of thedistillation column 3. This fraction comprises water (steam) as aprincipal component and is also accompanied by hydrogen sulfide. Thefraction from the top is guided to the condenser 5 through the line 4and cooled. The steam is turned into water by the cooling and stored inthe storage tank 6. In that case, hydrogen sulfide that is not condensedby the cooling is discharged through a line 7 as a non-condensable gascomponent without being stored in the storage tank. The discharge ofhydrogen sulfide permits the distillation column 3 to smoothly performdistillation. The hydrogen sulfide discharged may be recovered by anymethod such as absorption in an organic amide solvent.

In the method according to the present invention, a part of water storedin the storage tank 6 is refluxed into the distillation column 3. Inthat case, an amount of water refluxed is integrated by a flowmeter 9.The refluxing of a part of water within the storage tank 6 into thedistillation column 3 permits smoothly and efficiently performingseparation between the organic amide solvent and water by thedistillation column 3. In general, water refluxed is desirably refluxedinto the top or upper part of the distillation column.

With respect to water cooled, a part thereof may be refluxed into thedistillation column 3 without being stored in the storage tank 6, andthe remainder may be discharged through a line 8. Alternatively, a partof water that is not refluxed into the distillation column 3 may bestored within the storage tank 6, and the remainder may be dischargedthrough the line 8 when the capacity of the storage tank 6 is small. Inany event, the amount of water refluxed into the distillation column 3and the amount of water discharged without being refluxed are measured.After the dehydration step, water stored within the storage tank 6 maybe discharged through the line 8. Incidentally, the term “discharge” asused in the present invention means discharging outside the reactionvessel and the distillation column without being refluxed into bothdevices.

In the dehydration step, reflux conditions are set in such a manner thata weight ratio of the amount of water refluxed into the distillationcolumn to the amount of water discharged without being refluxed fallswithin a range of generally from 90:10 to 10:90, preferably from 80:20to 20:80, more preferably from 30:70 to 70:30.

Assuming that the amount of water refluxed into the distillation columnis R, the amount of water discharged without being refluxed is E, and aratio between them is R/E, a load upon heating in the distillationcolumn increases to cause energy loss as the ratio R/E becomes higher.If the ratio R/E is lower to the contrary, separation between theorganic amide solvent and water within the distillation column becomesdefective, so that a part of the organic amide solvent is distilled outtogether with water from the top of the distillation column anddischarged, which causes problems such as loss of the organic amidesolvent.

7. Calculation of Amount of Hydrogen Sulfide Volatilized:

In the present invention, an amount of water refluxed into thedistillation column in the dehydration step is measured by a flowmeter,and that amount is added to an amount (generally, an amount of waterstored in the storage tank) of water discharged without being refluxed.On the other hand, a relational expression between the total amount ofwater of the amount of water refluxed into the distillation column andthe amount of water discharged without being refluxed, and the amount(also referred to as “amount of hydrogen sulfide volatilized out”) ofhydrogen sulfide discharged is determined in advance, and the amount ofhydrogen sulfide discharged is calculated out from a measured value ofthe total amount of water on the basis of the relational expression.

Such a relational expression can be prepared by carrying out regressionanalysis using voluminous experimental data actually measured as to therelation between the total amount of water and the amount of hydrogensulfide volatilized out in the dehydration step as a database. When thedatabase is subjected to regression analysis, a relational expression ofa linear model or non-linear model (double logarithm model orsemilogarithm model) can be prepared. However, the relation between thetotal amount of water of the amount of water refluxed into thedistillation column and the amount of water discharged without beingrefluxed, and the amount of hydrogen sulfide discharged can beaccurately grasped by, for example, a linear model represented by thefollowing relational expression (I):y=ax+b  (I)wherein x is the total amount (amount of distillate of water) of theamount of water refluxed into distillation column and the amount ofwater discharged without being refluxed in the dehydration step, y isthe amount of hydrogen sulfide discharged from the reaction vessel, andboth a and b are parameters. In the relational expression (I), a and bare parameters varying according to the apparatus and operatingconditions a and b can be determined by subjecting the experimental datato regression analysis.

When the measured value (x) of the total amount of water is substitutedinto the relational expression (I), an amount (y) of hydrogen sulfidedischarged in the dehydration step can be calculated out. If the amountof hydrogen sulfide discharged in the dehydration step is known, anamount of the sulfur source remaining in the reaction vessel can becalculated out from that amount and the amount of the sulfur sourcecharged into the reaction vessel in the beginning.

In the present invention, thus, an amount (that is an actual “amount ofthe sulfur source charged”) of the sulfur source remaining in themixture after the dehydration step is calculated out on the basis of theamount of hydrogen sulfide calculated out to control a charged molarratio between the sulfur source (A) and the dihalo-aromatic compound (B)on the basis of the amount of the sulfur source (A) calculated out. Thecharged molar ratio between the sulfur source (A) and thedihalo-aromatic compound (B) is such that the amount of thedihalo-aromatic compound amounts to generally 0.90 to 1.50 mol,preferably 0.95 to 1.20 mol, more preferably 1.00 to 1.09 mol per mol ofthe sulfur source (alkali metal sulfide and/or alkali metalhydrosulfide). In order to obtain a PAS little in variation of meltviscosity every lot, it is desirable to fixedly control a molar ratio ofthe amount of the dihalo-aromatic compound charged to 1 mol of thesulfur source within a range of 1.00 to 1.09.

8. Polymerization Step:

The polymerization step is conducted by charging a dihalo-aromaticcompound into the mixture after completion of the dehydration step andheating the sulfur source and the dihalo-aromatic compound in an organicamide solvent. When a polymerization vessel different from the reactionvessel used in the dehydration step is used, the mixture after thedehydration step and the dihalo-aromatic compound are charged into thepolymerization vessel. After the dehydration step and before thepolymerization step, the amounts of the organic amide solvent andcoexisting water may be controlled as needed. Before the polymerizationstep or during the polymerization step, a polymerization aid and otheradditives may be mixed.

The mixing of the mixture obtained after completion of the dehydrationstep with the dihalo-aromatic compound is conducted within a temperaturerange of generally from 100 to 350° C., preferably from 120 to 330° C.When the respective components are charged into the polymerizationvessel, no particular limitation is imposed on the order of charging,and both components are charged in small portions or at a time.

The polymerization reaction is conducted at generally 100 to 350° C.,preferably 120 to 330° C., more preferably 170 to 290° C. As a heatingmethod for this reaction, is used a method of retaining a fixedtemperature, a method of raising the temperature either stepwise orcontinuously or a combination of both methods. The polymerizationreaction time is within a range of generally from 10 minutes to 72hours, desirably from 30 minutes to 48 hours. The amount of the organicamide solvent used in the polymerization step is within a range ofgenerally 0.1 to 10 kg, preferably 0.15 to 1 kg per mol of the chargedsulfur source existing in the polymerization step. The amount may bechanged in the course of the polymerization reaction so far as it fallswithin this range.

The content of water upon the beginning of the polymerization reactionis preferably controlled within a range of generally 0.3 to 5 mol permol of the sulfur source charged. When it is intended to obtain alow-molecular weight polymer or oligomer, or a special polymerizationprocess is adopted, however, the water content may be changed outsidethis range. For example, the water content may be controlled within arange of 0.1 to 15 mol, preferably 0.5 to 10 mol per mol of the sulfursource such as an alkali metal sulfide. The water content may beincreased in the course of the polymerization reaction or decreased bydistillation to the contrary.

Examples of polymerization processes comprising increasing the watercontent in the course of the polymerization reaction include a processcomprising conducting a reaction at a temperature of 170 to 270° C.,preferably 180 to 235° C. in the presence of water in an amount of 0.5to 2.4 mol, preferably 0.5 to 2.0 mol per mol of the sulfur sourcecharged to control a conversion of the dihalo-aromatic compound to 50 to98 mol %, adding water so as to bring about a state that water exists ina proportion of more than 2.0 mol, but up to 10 mol, preferably 2.5 to7.0 mol per mol of the sulfur source charged, and then heating thereaction system to a temperature of 245 to 290° C., thereby continuingthe reaction.

As a particularly preferable production process, may be mentioned aprocess comprising conducting a polymerization reaction in thepolymerization step by an at least two-stage polymerization processcomprising:

(1) Step 1 of heating a reaction mixture containing the organic amidesolvent, the sulfur source (A) and the dihalo-aromatic compound (B) to170 to 270° C. in the presence of water in an amount of 0.5 to 2.0 molper mol of the sulfur source (A) charged to conduct a polymerizationreaction, thereby forming a prepolymer that a conversion of thedihalo-aromatic compound is 50 to 98%, and

(2) Step 2 of controlling the amount of water in the reaction system soas to bring about a state that water exists in a proportion of more than2.0 mol, but up to 10 mol per mol of the sulfur source (A) charged, andheating the reaction system to 245 to 290° C., thereby continuing thepolymerization reaction.

In Step 1, it is desirable to form a prepolymer having a melt viscosityof 0.5 to 30 Pa·s as measured at a temperature of 310° C. and a shearrate of 1,216 sec⁻¹. In Step 2, the polymerization reaction is continuedso as to form a polymer having a melt viscosity higher than the meltviscosity of the prepolymer formed in Step 1.

Water may be added at a final stage of the polymerization reaction orupon completion thereof to increase the water content for the purpose oflowering the contents of common salt secondarily produced and impuritiesin the polymer formed or collecting the polymer in the form ofparticles. To the polymerization step according to the presentinvention, may be applied many of other publicly known polymerizationprocesses or modified processes thereof, and the present invention isparticularly not limited to a particular polymerization process. Thepolymerization reaction system may be a batch system, a continuoussystem or a combination of both systems. In the batch-wisepolymerization, 2 or more reaction vessels may be used for the purposeof shortening the polymerization cycle time.

In the production process according to the present invention, a posttreatment after the polymerization reaction may be conducted inaccordance with a method known per se in the art. For example, aftercompletion of the polymerization reaction, a product slurry cooled isseparated by filtration as it is or after diluted with water or thelike, and the resulting filter cake is washed and filtered repeatedly,and then dried, whereby a PAS can be collected. The product slurry maybe subjected to sieving as it is in a high-temperature state, therebycollecting the polymer. After the separation by filtration or sieving,the PAS may be washed with the same organic amide solvent as thepolymerization solvent, an organic solvent such as a ketone (forexample, acetone) or an alcohol (for example, methanol), hot water, orthe like. The PAS formed may also be treated with an acid or a salt suchas ammonium chloride.

No particular limitation is imposed on the melt viscosity (as measuredat a temperature of 310° C. and a shear rate of 1,216 sec⁻¹) of the PASaccording to the present invention. However, it is preferably within arange of 30 to 800 Pa·s, more preferably 40 to 500 Pa·s. When thepolymerization reaction is conducted by 2 stages, a PAS having a meltviscosity exceeding the melt viscosity of a prepolymer formed in thefirst-stage step (Step 1) is obtained in the second-stage step (Step 2).

The PASs obtained by the production process according to the presentinvention may be molded or formed into various injection-molded productsor extruded products such as sheets, films, fibers and pipes eithersingly or by incorporating various kinds of inorganic fillers, fibrousfillers and/or various kinds of synthetic resins, if desired, as it isor after oxidized and crosslinked. Since the PASs obtained by theprocess according to the present invention are little in lot-to-lotvariation of melt viscosity, the processing thereof can be stablyconducted, and the resulting formed or molded products are provided ashigh-quality products little in variations of various properties. ThePAS is particularly preferably poly(phenylene sulfide) (PPS).

EXAMPLES

The present invention will hereinafter be described more specifically bythe following Examples and Comparative Examples. Measuring methods ofphysical properties are as follows.

(1) Melt Viscosity:

A melt viscosity was measured by means of Capirograph 1-C (manufacturedby Toyo Seiki Seisakusho, Ltd.) using 20 g of a dry polymer as a sample.At this time, a flat die of 1 mm in diameter×10 mm in length was used asa capillary, and the temperature was set to 310° C. After the sample wasplaced in a measuring oven and held for 5 minutes, the melt viscositywas measured at a shear rate of 1,216 sec⁻¹.

Example 1

1. Dehydration Step:

An equipment shown in FIG. 1 was used to conduct a dehydration reactionas a step prior to a polymerization step. After 1,275 kg ofN-methyl-2-pyrrolidone (hereinafter abbreviated as “NMP”) was chargedinto a reaction vessel and heated to 150° C., 302 kg (3.45 kmol in termsof NaSH) of sodium hydrosulfide having a concentration of 64% by weightand 179 kg (3.36 kmol in terms of NaOH) of sodium hydroxide having aconcentration of 75% by weight were charged, and heating was conducteduntil the temperature within the reaction vessel reached 192° C. toconduct a dehydration reaction.

After the dehydration reaction, 120 kg of water was taken out into astorage tank 6. An amount of water refluxed into a distillation column 3during the dehydration reaction was integrated at 130 kg by a flowmeter9, and a total amount (hereinafter referred to as “amount of distillateof water”) of water passed through the distillation column 3 putting 120kg of water stored within the storage tank 6 together was calculated at250 kg.

From a database obtained by conducting the dehydration reactionrepeatedly many times, it is proven that a linear relation representedby the following relational expression (I):y=ax+b  (I)wherein both a and b are parameters, exists between an amount (y kg) ofhydrogen sulfide lost by being volatilized outside the reaction systemand the amount (x kg) of distillate of water upon the distillation inthe dehydration step by the distillation. Although a and b areparameters varying according to the apparatus and operating conditions,a was 0.0119, and b was −0.783 under the above-described experimentalconditions.

When the amount of distillate of water was 250 kg, the amount ofhydrogen sulfide volatilized out was calculated out at 2.2 kg (0.06kmol) from this relational expression (I). This value was used tocalculate out an amount of the sulfur source remaining in the reactionvessel and was found to be 3.38 kmol.

A trap composed of a 10% aqueous solution of NaOH was arranged in a line7 in FIG. 1 to determine an amount of hydrogen sulfide in the trap andstorage tank 6 by means of iodimetry so as to measure an S content lost.As a result, a value corresponding to 0.06 kmol was obtained and agreedwith the value calculated out by the method according to the presentinvention.

2. Polymerization Step:

This reaction vessel was charged with 503 kg (3.42 kmol) ofp-dichlorobenzene (hereinafter abbreviated as “pDCB”) to control a molarratio of PDCB to the sulfur source that is a monomer ratio to 1.012. Themixture within the reaction vessel was then heated up to 220° C. toconduct a reaction for 5 hours. The reaction vessel was then chargedwith 69 kg of water, and the reaction mixture was heated up to 260° C.to conduct a reaction for 5 hours.

After completion of the reaction, the reaction mixture was cooled nearto room temperature and sifted through a screen having a sieve openingof 150 μm (100 mesh) to collect a granular polymer formed. The granularpolymer was washed twice with acetone and additionally 3 times withwater to obtain a washed polymer. This washed polymer was immersed in a0.6% by weight aqueous solution of acetic acid to subject the polymer toan acid treatment. The thus-treated granular polymer was then washedtwice with water. The granular polymer was dried to obtain apoly(phenylene sulfide) having a melt viscosity of 140 Pa·s. The resultsare shown in Table 1.

Examples 2 to 10

A dehydration step was performed by the same apparatus and conditions asin Example 1 except that the amount of distillate of water was variedwithin a range of 250 to 350 kg by changing the reflux ratio in thedistillation column or changing the quantity of heating in the reactionvessel. After the dehydration step, an amount of distillate of water ineach case was substituted into the relational expression (I) tocalculate out an amount of hydrogen sulfide volatilized out, and anamount of the sulfur source remaining in the reaction vessel wascalculated out on the basis of that value. The reaction vessel wascharged with pDCB so as to give the same charged monomer ratio as inExample 1 on the basis of the amount of the sulfur source calculated outto perform the polymerization reaction and post treatment. Examples 2 to10 were experimental examples for confirming the effectiveness of theprocess according to the present invention in the case where the amountof distillate of water was set to about 300 kg. As the result of 10experiments in total including Example 1, the melt viscosities of thePPSs obtained were 124 Pa·s at the minimum, 155 Pa·s at the maximum and138 Pa·s (standard deviation: 9.7) on the average. The results are shownin Table 1.

Example 11

A dehydration step was performed by the same apparatus and conditions asin Example 1 except that the amount of distillate of water was changedto 500 kg. From the general expression (I), an amount of hydrogensulfide volatilized out was calculated out at 5.2 kg (0.15 kmol) whenthe amount of distillate of water was 500 kg. An amount of the sulfursource remaining in the reaction vessel was calculated out at 3.30 kmolfrom this value. The reaction vessel was charged with 490 kg (3.34 kmol)of pDCB so as to give the same charged monomer ratio as in Example 1 toperform the polymerization reaction and post treatment. As a result, PPShaving a melt viscosity of 139 Pa·s was obtained.

Example 12

A dehydration step was performed by the same apparatus and conditions asin Example 1 except that the amount of distillate of water was changedto 600 kg. From the general expression (I), an amount of hydrogensulfide volatilized out was calculated out at 6.4 kg (0.19 kmol) whenthe amount of distillate of water was 600 kg. An amount of the sulfursource remaining in the reaction vessel was calculated out at 3.26 kmolfrom this value. The reaction vessel was charged with 485 kg (3.30 kmol)of PDCB so as to give the same charged monomer ratio as in Example 1 toperform the polymerization reaction and post treatment. As a result, PPShaving a melt viscosity of 142 Pa·s was obtained. The results are shownin Table 1. TABLE 1 Amount of Amount of Amount of Monomer ratio Meltsulfur source Method of distillate S content lost pDCB upon viscositycharged calculating S of water upon dehydration charged polymerizationof PPS (kmol) content lost (kg) step (kmol) (H₂S) (kmol) (pDCB/S;mol/mol) (Pa · s) Ex. 1 3.45 Expression (I) 250 0.06 3.42 1.012 140 Ex.2 3.45 Expression (I) 330 0.09 3.40 1.012 131 Ex. 3 3.45 Expression (I)290 0.08 3.41 1.012 137 Ex. 4 3.45 Expression (I) 260 0.07 3.42 1.012128 Ex. 5 3.45 Expression (I) 350 0.10 3.39 1.012 141 Ex. 6 3.4Expression (I) 300 0.08 3.41 1.012 135 Ex. 7 3.45 Expression (I) 3200.09 3.40 1.012 124 Ex. 8 3.45 Expression (I) 250 0.06 3.42 1.012 133Ex. 9 3.45 Expression (I) 340 0.10 3.39 1.012 155 Ex. 10 3.45 Expression(I) 270 0.07 3.42 1.012 151 Ex. 11 3.45 Expression (I) 500 0.15 3.341.012 139 Ex. 12 3.45 Expression (I) 600 0.19 3.30 1.012 142

Comparative Examples 1 to 10

In Examples, the sulfur content lost (hereinafter abbreviated as “Scontent lost”) was calculated out from the amount of distillate of waterin the dehydration step, whereas in Comparative Examples 1 to 10, theamount of distillate of water was not investigated, and the amount ofPDCB charged was determined on the basis of the S content lost that hadbeen calculated out in Example 1 to conduct a polymerization reaction.In other words, the same equipment as in Examples 1 to 10 was used toconduct a dehydration reaction, a polymerization reaction and a posttreatment.

After 1,275 kg of NMP was charged into a reaction vessel and heated to150° C., 302 kg (3.45 kmol in terms of NaSH) of sodium hydrosulfidehaving a concentration of 64% by weight and 179 kg (3.36 kmol) of sodiumhydroxide having a concentration of 75% by weight were charged, andheating was conducted until the temperature within the reaction vesselreached 192° C. to conduct a dehydration reaction. Assuming that theamount of hydrogen sulfide volatilized out in the dehydration step is2.2 kg (0.06 kmol) like that calculated out in Example 1, an amount ofthe sulfur source remaining in the reaction vessel was calculated out at3.38 kmol using this value. The reaction vessel was charged with 503 kg(3.42 kmol) of pDCB on the basis of the amount of the sulfur source thuscalculated out to control a molar ratio of pDCB to the sulfur sourcethat is a monomer ratio to 1.012.

The mixture within the reaction vessel was heated up to 220° C. toconduct a reaction for 5 hours, the reaction vessel was then chargedwith 69 kg of water, and the reaction mixture was heated up to 260° C.to conduct a reaction for 5 hours. After completion of the reaction, thereaction mixture was cooled near to room temperature and sifted througha screen having a sieve opening of 150 μm (100 mesh) to collect agranular polymer. The granular polymer was washed twice with acetone andadditionally 3 times with water to obtain a washed polymer. This washedpolymer was immersed in a 0.6% by weight aqueous solution of aceticacid, washed additionally twice with water and then dried.

The melt viscosities of the respective polymers obtained by 10experiments (Comparative Examples 1 to 10) in total were 75 Pa·s at theminimum, 151 Pa·s at the maximum and 105 Pa·s (standard deviation: 22.6)on the average, so that a scatter of melt viscosity was extremely wide.The results are shown in Table 2.

Comparative Example 11

The calculation of the S content lost from the amount of distillate ofwater in the dehydration step according to the present invention was notconducted, and a trap composed of a 10% aqueous solution of NaOH wasarranged in the line 7 in FIG. 1 to determine an amount of hydrogensulfide in the trap and storage tank 6 by means of iodimetry so as todetermine an S content lost.

After 1,275 kg of NMP was charged into a reaction vessel and heated to150° C., 302 kg (3.45 kmol in terms of NaSH) of sodium hydrosulfidehaving a concentration of 64% by weight and 179 kg (3.36 kmol) of sodiumhydroxide having a concentration of 75% by weight were charged, andheating was conducted until the temperature within the reaction vesselreached 192° C. to conduct a dehydration reaction. After the dehydrationreaction, iodimetric analysis was conducted on the collection solution.As a result, an amount of hydrogen sulfide volatilized out wasdetermined at 0.10 kmol. From this value, an amount of the sulfur sourceremaining in the reaction vessel was calculated out at 3.35 kmol. Thereaction vessel was charged with 498 kg (3.39 kmol) of pDCB on the basisof this amount of the sulfur source to control a molar ratio of pDCB tothe sulfur source that is a monomer ratio to 1.012.

The mixture within the reaction vessel was heated up to 220° C. toconduct a reaction for 1 hour, and then heated up to 230° C. over 30minutes to conduct the reaction additionally for 1.5 hours. The reactionvessel was then charged with 69 kg of water, and the reaction mixturewas heated up to 260° C. to conduct a reaction for 5 hours. Aftercompletion of the reaction, the reaction mixture was cooled near to roomtemperature and sifted through a screen having a sieve opening of 150 μm(100 mesh) to collect a granular polymer. The granular polymer waswashed twice with acetone and additionally 3 times with water to obtaina washed polymer. This washed polymer was immersed in a 0.6% by weightaqueous solution of acetic acid, washed additionally twice with waterand then dried. The melt viscosity of the PPS obtained was 142 Pa·s. Theresults are shown in Table 2. TABLE 2 Amount of Amount of Amount ofMonomer ratio Melt sulfur source Method of distillate S content lostpDCB upon viscosity charged calculating S of water upon dehydrationcharged polymerization of PPS (kmol) content lost (kg) step (kmol)(kmol) (pDCB/S; mol/mol) (Pa · s) Comp. 3.45 Calculated at — 0.06 3.42 —122 Ex. 1 a fixed value (assumed value) Comp. 3.45 Calculated at — 0.063.42 — 88 Ex. 2 a fixed value (assumed value) Comp. 3.45 Calculated at —0.06 3.42 — 105 Ex. 3 a fixed value (assumed value) Comp. 3.45Calculated at — 0.06 3.42 — 93 Ex. 4 a fixed value (assumed value) Comp.3.45 Calculated at — 0.06 3.42 — 121 Ex. 5 a fixed value (assumed value)Comp. 3.4 Calculated at — 0.06 3.42 — 151 Ex. 6 a fixed value (assumedvalue) Comp. 3.45 Calculated at — 0.06 3.42 — 82 Ex. 7 a fixed value(assumed value) Comp. 3.45 Calculated at — 0.06 3.42 — 102 Ex. 8 a fixedvalue (assumed value) Comp. 3.45 Calculated at — 0.06 3.42 — 112 Ex. 9 afixed value (assumed value) Comp. 3.45 Calculated at — 0.06 3.42 — 75Ex. 10 a fixed value (assumed value) Comp. 3.45 Analysis — 0.10 3.391.012 142 Ex. 11 (analyzed value)

INDUSTRIAL APPLICABILITY

According to the present invention, in the production process of apoly(arylene sulfide) comprising the polymerization step of subjecting asulfur source and a dihalo-aromatic compound to a polymerizationreaction in an organic amide solvent, a dehydration step that is a priorstep can be smoothly performed, and a molar ratio of the sulfur sourcecharged to the dihalo-aromatic compound charged can be accurately set onthe basis of the relational expression between an amount of hydrogensulfide volatilized out of the reaction system and lost and an amount ofdistillate of water upon distillation, thereby stably producing apoly(arylene sulfide) having a desired melt viscosity.

1. A process for producing a poly(arylene sulfide), comprising, after adehydration step of heating and dehydrating a mixture containing anorganic amide solvent, at least one sulfur source (A) selected from thegroup consisting of alkali metal hydrosulfides and alkali metal sulfidesand an alkali metal hydroxide added as needed to control the amount ofwater in the mixture, a polymerization step of charging adihalo-aromatic compound (B) into the system containing the remainingmixture to subject the sulfur source (A) and the dihalo-aromaticcompound (B) to a polymerization reaction in the organic amide solvent,which comprises: (1) in the dehydration step, heating the mixturecontaining the organic amide solvent, at least one sulfur source (A)selected from the group consisting of alkali metal hydrosulfides andalkali metal sulfides and the alkali metal hydroxide added as needed ina reaction vessel, to which a distillation column is linked, and guidingvapor volatilized to the distillation column to distill and separate itinto respective components, refluxing a fraction taken out of the bottomof the distillation column and comprising the organic amide solvent as aprincipal component into the reaction vessel, cooling a fraction takenout of the top of the distillation column and comprising water andhydrogen sulfide to discharge hydrogen sulfide that is not condensed bythe cooling and reflux a part of water condensed into the distillationcolumn, discharging the remaining water, (2) determining a relationalexpression between the total amount of water of an amount of waterrefluxed into the distillation column and an amount of water dischargedwithout being refluxed, and an amount of hydrogen sulfide dischargedfrom the reaction vessel in advance, thereby calculating out an amountof hydrogen sulfide discharged from the reaction vessel from a measuredvalue of the total amount of water on the basis of the relationalexpression, (3) calculating out an amount (hereinafter referred to as“amount of the sulfur source charged”) of the sulfur source (A)remaining in the mixture after the dehydration step on the basis of theamount of hydrogen sulfide calculated out, thereby controlling a chargedmolar ratio of the sulfur source (A) to the dihalo-aromatic compound (B)on the basis of the amount of the sulfur source (A) calculated out, andthen (4) subjecting the sulfur source (A) and the dihalo-aromaticcompound (B) to the polymerization reaction in the organic amide solventin the polymerization step.
 2. The production process according to claim1, wherein the relational expression is a linear relational expressionrepresented by the following relational expression (I):y=ax+b  (I) wherein x is the total amount of the amount of waterrefluxed into distillation column and the amount of water dischargedwithout being refluxed in the dehydration step, y is the amount ofhydrogen sulfide discharged from the reaction vessel, and both a and bare parameters.
 3. The production process according to claim 1, whereinin the dehydration step, the mixture is heated to a temperature of 100to 250° C.
 4. The production process according to claim 1, wherein inthe dehydration step, reflux conditions are set in such a manner that aweight ratio of the amount of water refluxed into the distillationcolumn to the amount of water discharged without being refluxed fallswithin a range of from 90:10 to 10:90.
 5. The production processaccording to claim 1, wherein in the dehydration step, the dehydrationunder heat is conducted in such a manner that the water content fallswithin a range of 0.3 to 5 mol per mol of the alkali metal sulfide (A)charged.
 6. The production process according to claim 1, wherein in thedehydration step, the dehydration under heat is conducted by means of anapparatus so constructed that an upper part of the reaction vessel isconnected to the distillation column, a fraction from the top of thedistillation column is successively sent to a condenser and a storagetank, a fraction from the bottom of the distillation column is refluxedinto the reaction vessel, a part of water stored in the storage tank isrefluxed into the distillation column, and at that time an amount ofwater refluxed is integrated by a flowmeter.
 7. The production processaccording to claim 1, wherein after the dehydration step, an amount ofthe dihalo-aromatic compound (B) charged is controlled within a range of1.00 to 1.09 mol per mol of the sulfur source (A) charged.
 8. Theproduction process according to claim 1, wherein in the polymerizationstep, the polymerization reaction is conducted by an at least two-stagepolymerization process comprising: (1) Step 1 of heating a reactionmixture containing the organic amide solvent, the sulfur source (A) andthe dihalo-aromatic compound (B) to 170 to 270° C. in the presence ofwater in an amount of 0.5 to 2.0 mol per mol of the sulfur source (A)charged to conduct a polymerization reaction, thereby forming aprepolymer that a conversion of the dihalo-aromatic compound is 50 to98%, and (2) Step 2 of controlling the amount of water in the reactionsystem so as to bring about a state that water exists in a proportion ofmore than 2.0 mol, but up to 10 mol per mol of the sulfur source (A)charged, and heating the reaction system to 245 to 290° C., therebycontinuing the polymerization reaction.
 9. The production processaccording to claim 8, wherein in Step 1, a prepolymer having a meltviscosity of 0.5 to 30 Pa·s as measured at a temperature of 310° C. anda shear rate of 1,216 sec⁻¹ is formed.